|Kayaba "Ka"-Go / Ka-1|
Although relatively unknown the Kayaba Ka-1 autogyro deserves a special place in aviation history since it was the first armed machine of the autogyro/helicopter family to have been used operationally.
In the late thirties the Imperial Japanese Army began to show considerable interest in the use of the autogyro as an artillery spotter and in 1939 a Kellet KD-1A single-engined two-seat autogyro was imported from the United States. Powered by a 225hp Jacobs L-4M4 seven-cylinder air-cooled radial, the KD-1A featured an advanced version of the Kellet direct control rotor system. Unfortunately, shortly after its arrival in Japan, the aircraft was seriously damaged during flight trials at low speeds. The Kellet KD-1A had been damaged beyond repair, but the Japanese Army delivered the wreck to K.K. Kayaba Seisakusho (Kayaba Industrial Co Ltd), a small company doing autogyro research, with instructions to develop a similar machine.
At the request of the Koku Hombu the Kayaba engineering team developed a two-seat observation autogyro based on the Kellet KD-1A but modified to Japanese production standards. Designated Ka-1, this autogyro was powered by a 240hp Argus As 10c eight-cylinder inverted-vee air-cooled engine driving a two-blade propeller, and had a three-blade rotor. Completed in May 1941 at the Sendai (Miyagi Prefecture) plant of Kayaba, the first Ka-1 made its maiden flight at Tamagawa on 26 May, 1941. During its flight test programme the Ka-1 performed remarkably well, demonstrating its ability to take-off after running only 30m in still air. By running the engine at full power and holding the nose 15° up, the Ka-1 could hover and could also execute a full 360° turn while hovering. As maintenance in the field appeared to present less difficulty than anticipated the aircraft was placed in production for service with artillery units.
When shipping losses began to rise alarmingly the Japanese Army commissioned the light escort carrier Akitsu Maru, a converted merchant ship. The short take-off characteristics of the Ka-1 rendered it suitable for operation from this small vessel and accordingly a small number of Ka-ls were modified as anti-submarine patrol aircraft. As the load-carrying capability of the standard two-seat Ka-1 was too limited, the carrier-borne Ka-ls were operated as single-seaters and carried two 60kg depth-charges. In this role the Ka-ls operated over Japanese coastal waters and particularly over the Tsugara and Korean channels. At least one of these aircraft, the Ka-1 KAI, was tested with powder rockets on the rotor tips in an attempt to improve its load-carrying capability while another aircraft was fitted with a 240hp Jacobs L-4MA-7 seven-cylinder air-cooled radial. With Jacobs engine the type became the Ka-2.
R.J.Francillon "Japanese Aircraft of the Pacific War", 1970
The Japanese government, after acquiring and testing a Kellett KD-1A autogyro in 1939, turned the aircraft over to the Kayaba Industrial Co, which subsequently built an inline-engined version of the aircraft as the Ka.1. This was powered by a 240hp Kobe engine (licence version of the German Argus As.10C); the first Ka.1 was flown on 26 May 1941 and eventually some two hundred and forty aircraft of this type were built. They were employed during World War 2 by the Imperial Japanese Army for artillery observation and cooperation duties, and by the Navy for coastal or carrier-based antisubmarine patrol carrying two 60kg bombs or depth charges. One Ka.1 was modified for trials with small auxiliary rockets at the tips of the rotor blades.
K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968
Technical data for Kayaba Ka-1
Engine: 1 x "Argus" As 10c pistone engine, rated at 180kW, main rotor diameter: 12.2m, take-off weight: 1170kg, empty weight: 775kg, max speed: 165km/h, cruising speed: 115km/h, ceiling: 3500m, range: 280km, armament: 2 x 60kg depth charges